Conventionally, in consideration of the rapidity of chemical reactions, and the need to carry out reactions using very small amounts, on-site analysis and the like, integration technology for carrying out chemical reactions in very small spaces has been focused upon, and research into this technology has been carried out with vigor throughout the world.
An example of such integration technology for carrying out chemical reactions is so-called microchemical systems that carry out mixing, reaction, separation, extraction, detection or the like on a sample placed in a very narrow channel which is formed in a small glass substrate or the like. Examples of reactions carried out in the microchemical systems include diazotization reactions, nitration reactions, and antigen-antibody reactions. Examples of extraction/separation include solvent extraction, electrophoretic separation, and column separation. Such a microsystem may use only a single function intended to carry out separation alone, or may use a plurality of functions in combination.
As an example in which ‘separation’ is the sole aim, out of the above functions, an electrophoresis apparatus for analyzing extremely small amounts of proteins, nucleic acids or the like has been proposed (e.g. Japanese Laid-open Patent Publication (Kokai) No. 8-178897). This electrophoresis apparatus analyzes extremely small amounts of proteins, nucleic acids or the like and is provided with a channel-formed plate-shaped element comprised of two glass substrates joined together. Because the element is plate-shaped, breakage is less likely to occur than in the case of a glass capillary tube having a circular or rectangular cross section, and hence handling is easier.
In these microchemical systems, because the amount of the sample is very small, a high-precision detection method is essential. The path to making a detection method of the required precision fit for practical use has been opened up through the establishment of a photothermal conversion spectroscopic analysis method which utilizes a thermal lens effect that is produced through a liquid-borne sample absorbing light in a very narrow channel.
When light is convergently irradiated onto a sample, the temperature of a solvent is locally increased by thermal energy emitted due to light absorbed by a solute in the sample to cause a change in the refractive index and hence generate a thermal lens (photothermal conversion effect). The photothermal conversion spectroscopic analysis method utilizes this photothermal conversion effect.
FIG. 6 is a view useful in explaining the principle of a thermal lens.
In FIG. 6, a convergent beam of exciting light is irradiated onto an extremely small sample via an objective lens of a microscope, whereupon the photothermal conversion effect takes place. In the sample onto which the convergent beam of exciting light is irradiated, the center of the convergent beam of exciting light is where the temperature rise is highest, and hence the rise rate of the temperature is greater toward the center of the convergent beam of exciting light, whereas the rise rate of the temperature is smaller with increasing distance from the center of the convergent beam of exciting light due to thermal diffusion. For most substances, the refractive index drops as the temperature rises, and hence the drop rate of the refractive index of the sample is greater toward the center of the convergent beam of exciting light, whereas the drop rate of the refractive index of the sample is smaller with increasing distance from the center of the convergent beam of exciting light. Optically, this pattern of change in the refractive index brings about the same effect as with a concave lens, and hence the effect is called the thermal lens effect. The size of the thermal lens effect, i.e. the power of the thermal lens is proportional to the optical absorbance of the sample. Moreover, in the case that the refractive index increases with temperature, a converse effect to the above, i.e. the same effect as a convex lens is produced.
In the photothermal conversion spectroscopic analysis method described above, thermal diffusion in a sample, i.e. change in refractive index of the sample, is observed, and hence the method is suitable for detecting concentrations in extremely small amounts of samples.
A photothermal conversion spectroscopic analyzer that uses the photothermal conversion spectroscopic analysis method described above has been proposed by Japanese Laid-open Patent Publication (Kokai) No. 10-232210.
In the conventional photothermal conversion spectroscopic analyzer, a channel-formed plate-shaped element is disposed below the objective lens of a microscope, and exciting light of a predetermined wavelength outputted from an exciting light source is introduced into the microscope. The exciting light is thus convergently irradiated via the objective lens onto a sample in the channel of the channel-formed plate-shaped element. Thus, a thermal lens is formed about the convergent irradiation position in which the exciting light is convergently irradiated.
Moreover, detecting light having a wavelength different to that of the exciting light is outputted from a detecting light source and also introduced into the microscope and then emitted therefrom. The detecting light emitted from the microscope is convergently irradiated onto the thermal lens that has been formed in the sample by the exciting light. Then, the detecting light passing through the sample is either diverged or converged due to the effect of the thermal lens. The diverged or converged light exiting the sample passes as signal light through a converging lens and a filter or just a filter, and is then received and detected by a detector. The intensity of the detected signal light depends on the refractive index of the thermal lens formed in the sample. The detecting light may have the same wavelength as that of the exciting light, or the exciting light may be used as the detecting light as well.
In the spectroscopic analyzer described above, a thermal lens is thus formed at the focal position of the exciting light, and the change in refractive index within the formed thermal lens is detected by means of detecting light.
In the above photothermal conversion spectroscopic analyzer, the light source, measuring section and detecting section (photothermal conversion section) have complicated optical systems and hence are large in size and lacks portability. Thus, in carrying out analysis or handling chemical reactions using the photothermal conversion spectroscopic analyzer, there are limitations on the place for installing the analyzer and the operation of the analyzer, and even the working efficiency of the user is degraded.
Further, in the above photothermal conversion spectroscopic analyzer, the exciting light and the detecting light are guided in the air to the sample, and therefore, optical elements such as the light source, mirrors, and lenses are fixed to a solid surface table to prevent these optical elements from moving during measurement. Moreover, in the case that the optical axes of the exciting light and the detecting light are shifted due to environmental changes such as temperature change, a jig is required for correcting the shifting. These also constitute factors of the increased size of the photothermal conversion spectroscopic analyzer and the lack of portability of the same.
In a microchemical system using the photothermal conversion spectroscopic analysis method, in most cases, it is required that the focal position of the exciting light and that of the detecting light should be different from each other. FIGS. 7A and 7B are views useful in explaining the formation position of the thermal lens and the focal position of the detecting light in the direction of travel of the exciting light. FIG. 7A shows a case in which the objective lens has chromatic aberration, whereas FIG. 7B shows a case in which the objective lens does not have chromatic aberration.
In the case that the objective lens 130 has chromatic aberration, a thermal lens 131 is formed at the focal position 132 of the exciting light as shown in FIG. 7A. The focal position 133 of the detecting light is shifted by an amount ΔL from the focal position 132 of the exciting light, and thus changes in the refractive index within the thermal lens 131 can be detected as changes in the focal distance of the detecting light from the detecting light. In the case that the objective lens 130 does not have chromatic aberration, on the other hand, the focal position 133 of the detecting light is almost exactly the same as the position of the thermal lens 131 formed at the focal position 132 of the exciting light, as shown in FIG. 7B. The detecting light is thus not deflected by the thermal lens 131, and hence changes in the refractive index within the thermal lens 131 cannot be detected.
However, the objective lens of a microscope is generally manufactured so as not to have chromatic aberration, and hence the focal position 133 of the detecting light is almost exactly the same as the position of the thermal lens 131 formed at the focal position 132 of the exciting light as described above, as shown in FIG. 7B. Changes in the refractive index within the thermal lens 131 thus cannot be detected. There is thus a problem that trouble must be taken to either shift the position in which the thermal lens 131 is formed from the focal position 133 of the detecting light every time a measurement is taken as shown in FIGS. 8A and 8B, or else angle the detecting light slightly using a lens (not shown) before passing the detecting light through the objective lens 130 so that the focal position 133 of the detecting light will be shifted from the thermal lens 131 as shown in FIG. 9. This also leads to degraded working efficiency of the user.
It is an object of the present invention to provide a microchemical system and a photothermal conversion spectroscopic analysis method implemented by the microchemical system which enable working efficiency of the user to be improved, and also provide a microchemical system which can be made smaller in size.